Without limiting the scope of the invention, its background is described in connection with current methods of etching mercury cadmium telluride.
Mercury cadmium telluride, hereafter referred to as MCT, has been widely used to detect infrared radiation. FLIR (forward looking infrared) systems produce a visible image of an infrared scene, providing the ability to see variations in temperature in the absence of visible illumination. Such systems have been used for `night vision` by the military for many years, and many FLIR systems use MCT as the detector material. MCT has an electronic bandgap which is well suited to the detection of infrared photons. The bandgap may be adjusted by varying the ratio of mercury to cadmium, giving a range of wavelength sensitivity from less than 3 microns to more than 14 microns. MCT is frequently fabricated into linear arrays which are scanned in the focal plane of an imaging optical system in order to sense the two-dimensional infrared scene, or two-dimensional `starring` focal plane arrays of MCT detectors may be fabricated to sense the scene without mechanical scanning. Such arrays may be fabricated on a semiconductor substrate which may provide, for example, electrical connections and/or signal conditioning functions. Signals from the detectors are then typically represented on a display as a grey-scale image, each pixel of which represents the infrared intensity at the corresponding location in the scene.
MCT generally must be patterned during the fabrication of both discrete detector devices and linear and two-dimensional arrays of detectors. Patterning of the MCT material is a critical step in the manufacture of these devices and systems. Heretofore, in this field, MCT has been patterned in a variety of ways. MCT may be etched in bromine, typically 1 to 5 percent Br.sub.2 in a methanol solution. Plasma etching and ion milling of MCT with hydrocarbon or halogen reagents are also known.